Gas-Liquid Two-Phase Flow And Mass Transfer Of CO₂ Absorption In Microchannels

In recent years,micro-chemical technology has received increasing attention due to its good performance in heat transfer,mass transfer,and chemical reaction.It is an important basis to stud y gas-liquid two-phase flow and mass transfer in microchannel for industrial application and technical development.In this paper,the high speed camera and pressure sensor were used to investigate experimentally gas-liquid two-phase flow and mass transfer performance in microchannels.The pressure drop,bubbles frequency,bubble initial volume,and bubble velocity for gas-liquid two-phase flow in microchannel was investigated.The pressure drop was obtained by measuring pressure at inlet and outlet of microchannel.The pressure drop increases with the increase of gas and liquid velocities and decreases with the increase of CO2 concentration in gas phase.A pressure drop prediction equation was proposed.The bubble frequency increases with the increase of gas and liquid velocity.A bubble frequency prediction equation was proposed.The bubble initial volume increases with the increase of gas flow and decreases with the increase of liquid flow.A prediction equation was proposed to estimate the bubble initial volume.The total gas-liquid specific surface area in the microchannel was calculated.The specific area increases with the increase of the ratio of gas and liquid flow.Little influence of total gas-liquid two-phase flow rate on the specific area was observed.The bubble velocity was found in the experiment range is always faster than the total two-phase flow velocity,and the difference between them increases with the increase of gas and liquid flow rates.The gas-liquid mass transfer was investigated exp erimentally.The mass transfer coefficient of the mass transfer process was calculated by means of image analysis method.In the range of the experiment,mass transfer coefficient increases with gas flow,liquid flow,reactant concentration,and CO2 concentration in gas phase.The mass transfer was controlled by both chemical reaction and gas-side mass transfer resistance.A correlation was proposed to predicted mass transfer coefficient.An online method was used to study the evolution of bubble volume dur ing the mass transfer process.The influences of operating condition,reactant concentration,CO2 concentration on the evolution of bubble volumes were investigated experimentally.Moreover,the absorption and mass transfer characteristic in the bubble formation stage was investigated.The mass transfer during bubble formation stage accounts for 18%-48% of the total mass transfer of whole process.A correlation was proposed to predict mass transfer coefficient of bubble formation stage.Furthermore,the instantaneous mass transfer rate of CO2 absorption process was studied by dividing the microchannel into a lot of segments.The evolutions of CO2 residual quantity,mass transfer coefficient and the surface area of bubbles were studied,and a predicting method for calculating the instantaneous mass transfer coefficient was developed based on the evolution regulation durong the mass transfer process.